Azo compounds containing carboxyl and cyano groups



Patented Aug. 29, 1950 AZO COMPOUNDS CONTAINING CARBOXYL AND CYANO GROUPS James A. Robertson, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington,

Del., a corporation of Delaware No Drawing. Application June 27, 1947, Serial No. 757,682

4 Claims.

This invention relates to new aliphatic azo compounds containing carboxyl and nitrile groups and to the use thereof in the addition polymerization of polymerizable organic compounds. 7

Compounds containing directly-linked oxygen atoms, such as benzoyl and other peroxides have been widely used as polymerization catalysts. They provide a source of ozygen which may change the properties of the polymer obtained, for example, by discoloration, oxidation of added dyestuffs, and insolubilization. l

A new class of catalysts has been described in Hunt U. S. Patent No. 2,471,959, which issued May 31, 1949. on an application which was a continuation-in-part of abandoned application,

Serial. Number 655,015, filed March 16, 1946, which are advantageous in that they do not promote discoloration and do not provide a source of oxygen for oxidation of added dyestuffs or insolubilization. However, the aliphatic azo compounds specifically disclosed in said application Serial Number 655,015 are not water-soluble and do not readily give dispersions of polymeric materials when polymerizations are carried out in the presence of water. For many applications, polymer dispersions in water are of advantage.

This invention has as an object the prepara-- tion of a new class of azonitriles. A further object is the preparation of water-soluble addition polymerization catalysts. Other objects will appear hereinafter.

Broadly speaking, these objects are accomplished by the invention of carboxyl-containing azonitriles and their salts. More specifically the am compounds of this invention are those in which at least one or the nitrogens in the azo group (-N=N) is attached to a tertiary carbon atom which has attached thereto a nitrile group and a hydrocarbon radical containing, as a substituent, a carboxyl group as such or in the form of one of its salts, i. e. a group --COOY where Y is a monovalent cation. The nature of the radical to which the remainingnitrogen of the azo group is attached is not critical but preferably it is the same as that attached to the other azo nitrogen.

. The azo compounds of the present invention can beprepared by treating an oxo-carbonyl compound which also contains a carboxylic group, preferably as a water-soluble salt, with hydrazine followed by reaction with hydrogen cyanide. The resultant hydrazo compound can be oxidized with chlorine or bromine to the desired carboxylcontaining azonitrile (or its salt).

Example I A 25% aqueous solution of 138 parts of sodium levulinate was mixed with 25 parts of hydrazine hydrate and the solution heated on a steam bath for 6 hours. The mixture was cooled and treated with parts of liquid hydrogen cyanide and was allowed to stand about 16 hours at room temperature. Excess hydrogen cyanide was removed by bubbling a stream of nitrogen through the solution. The solution was then treated with a stream of chlorine gas until halogen was no longer absorbed. The solid which formed was collected on a filter and purified by dissolving inaqueous sodium hydroxide followed by precipitation by dilute hydrochloric acid. After drying in a vacuum desiccator, the solid alpha,alpha'- azobis(alpha-methyl gamma-carboxybutyronitrile) obtained weighed 92 parts corresponding to a 66% yield. The azonitrile melted at -123" C. with dec. and had the following analysis: Calculated for C12H15N4Ot: C, 51.4; H, 5.7; N, 20.0; neutral equivalent, 140. Found: C, 51.3; H, 5.7; N, 20.4; neutral equivalent 141.5.

Example II A container was charged with 50 parts of vinyl acetate, 150 parts of water, 0.5 parts of potassium monoacid phosphate, 1.5 parts of sodium dodecylsulfate and 0.5 parts of alpha,alpha azobis(alpha-methyl amma carboxybutyronitrile). The container was closed and heated with rocking in a water bath for 40 hours at 40 C. Unreacted monomer was removed from the resulting polyvinyl acetate dispersion by distillation with steam and the polymer was coagulated with saltsolution, washed thoroughly with water. and dried by milling at -450 C. on a rubber mill. There was obtained 37 parts corresponding to a 74% yield of polymer which had a relative viscosity of 1.609 in chloroform at a concentration of 0.1 g./100 ml. of solution at 25 C. The polymer prepared with the amnitrile catalyst dissolved readily in hot methanol to give solutions free of gel while comparable polymers prepared with ammonium persulfate as the catalyst dissolved with difficulty and gave aoeaaaa solutions containing many gel particles. During the milling operation, polymers prepared with colored.

Example III Example IV In a pressure resistant stainless steel vessel capable of containing 400 parts of water was placed 80 parts of benzene and 0.1 part of alpha,alphaazobis alpha methyl gamma carboxybutyronitrile). The vessel was flushed with nitrogen, the nitrogen was evacuated and the vessel was pressured to 400 atmospheres with ethylene. The reaction vessel with contents was heated at 120 C. for hours while the ethylene pressure was maintained at 840-915 atmospheres. The reactor was cooled, bled of excess ethylene, and

opened. The polymer was dried by milling at 140 C. on a rubber mill. There was thus obtained 14 parts of polyethylene which had relative viscosity of 1.140 as determined in xylene at 85 C. and a concentration of 0.125 g./ 100 ml. of solution. The polymer had a tensile strength of 3310 lbs/sq. in. with an elongation at break of 720% and a bending modulus of 31,000 lbs/sq. in.

The present invention is generic to carboxylcontaining azonitriles and in particular it is generic to azo compounds in which at least one of the nitrogens of the azo, N=N, group is attached to a tertiary carbon which has attached thereto a nitrile group and a hydrocarbon radical containing, as a substituent, a carboxyl group as such or in the form of one of its salts, i. e. a group COOY where Y is a monovalent cation. The nature of the radical to which the remaining nitrogen of the azo group is attached is not critical but preferably it is the same as that attached to the other azo nitrogen. Preferably the two radicals attached to the azo, N=N, group are, except for the, CN and -COOY groups, hydrocarbon.

The azonitriles of this invention contain the group COOY, where Y is a monovalent cation. Although the azonitrile compounds containing a carboxylic acid group, i. e. where Y is H, are usually sufficiently water-soluble to serve as polymerization catalysts in water systems, it is preferred from the standpoint of.water-solubility that water-soluble salts of these compounds be used, even though they are generally somewhat less active as catalysts. The salts are preferably the alkali metal and ammonium salts including the sodium, lithium, potassium and quaternary ammonium salts, e. g. the tetramethyl ammonium salt.

Particularly useful are the azonitriles in which both azo nitrogens are attached to aliphatic carbons and the caboxyl group is attached to a carbon at least 3 carbons removed from the azo 111- hood of 12 to 24 hours.

trogen. Such compounds can be represented by the formula RHC(COOY) CH2C(R1) (CN)N= NC(CN) (R1) CH:C(COOY)HR where Y is a monovalent cation, e. g. hydrogern an alkali metal or the ammonium group, R1 is an organic radical preferably a hydrocarbon radical of 1-6 carbons, and the R is hydrogenor a hydrocarbon radical of 1-6 carbons. The invention is generic to compounds of this formula.

Specific examples of such compounds are alpha,alpha-azobis(alpha methyl gamma carboxybutyronitrile) alpha,alpha ambiflalphap gamma,gamma-trimethyl gamma carbonbntyronitrile), alpha,alpha'-azobls(alpha-methylgamma phenyl gamma-carboxybutyronitrilel, alpha,alpha'-azobis (alpha-propyl gamma carboxybutyronitrile). In general the more useml azonitriles have organic groups of from 8-12 carbons attached to each of the azo nitrogens.

These compounds can be prepared by the ifollowing steps: (a) treatment of an alkali salt or the carboxyl-containing ketone with hydrazine in aqueous medium to form the azine. (b) treatment of the resultant azine in aqueous medium with hydrogen cyanide to form the corresponding hydrazonitrile, and (0) oxidation of the hydrazonitrile with chlorine or bromine to give the carboxyl-containing azonitrile. Step 6 is preferably carried out at moderately elevated temperatures. e. g, on a steam bath. At this temperature 0.), the reaction is, in general, essentially complete in six hours. At lower temperatures, e. g. 30 0., longer reaction times are required. Step b is conveniently carried out at room temperature, the time of reaction at this temperature (20-30 0.) being in the neighbor- Temperatures outside this range, e. g. 10 to 50 C.. can be used however. The oxidation step c is carried out by introducing chlorine or bromine into a stirred solution of the hydrazo compound at low temperatures, e. g. 5 to 10 C. At higher temperatures the yield of azo compound is poorer, whereas at lower temperatures there is danger that the mixture will freeze. The chlorine or bromine is introduced until absorption thereof ceases. Step c also converts the alkali salt of the carboxyl groups present in the azo compound to the free carboxyl groups. The carboxyl-containing azonitrile can be purified by crystallization or by conversion into a more soluble salt followed by precipitation as the free acid from an aqueous solution of the salt.

The azonitriles of this invention are of utility as catalysts for chain reactions, e. g. chlorination, and chlorosulfonation, and particularly polymerization catalysts in the addition polymerization, including copolymerlzation, of polymerizable compounds containing ethylenic double bonds. Numerous compounds of this type are known in the art. Examples include monoolefins, such as ethylene, isobutylene and styrene; dioleilns, particularly butadiene; vinyl esters, e. g. vinyl chloride, vinyl fluoride, vinyl acetate, vinyl propionate; vinylidine halides, e. g. vinylidene chloride and fluoride; vinyl ether: and ketones, e. g. vinyl butyl ether and methyl vinyl ketone; acrylyl and methacrylyl compounds, e. g. acrylonitrile, methyl methacrylate. and methacrylamide; polyfluoroolefins, e. g. tetrafiuoroethylene, triiiuorochloroethylene and 1,1 difluoro 2,2 dichloroethylene; and compounds containing two or more isolated or 00njugated double bonds, e. g. the dlacrylic acid esters of glycols and polyethylene glycols, for example, tetraethylene glycol dimethacrylate, diallyl diglycolate, diallyl carbonate, diallyl phthalate, ethylene bis-(allyl maleate), chloroprene, and fluoroprene. A particularly important group, to which the majority of the above polymerizable compounds belong, is that of polymerizable compounds having a CH2=C= groupi The amount of the azonitrile to e employed varies between 0.001 and 5% based the weight of polymerizable compounds present although usually between 0.1 and 3% is used. The temperature usually employed is 20125 C. or higher. Lower temperatures can be used when light is employed in conjunction with the azonitrile. The polymerization can be. carried out in bulk or emulsion systems. The water-soluble character of salts of the azonitriles of this invention permit them to be used with particular advantage in water systems.

In addition to the use of the azonitriles of this invention as polymerization catalysts, decomposition of the azonitriles by heating until nitrogen is evolved produces the corresponding dinitriles in which the nitrile groups are attached to ad jacent carbons. Such dinitriles may be used as intermediates in organic reactions.

The foregoing detailed description has been no unnecessary limitations are to be understood therefrom. ,The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

What is claimed is:

1. An azo compound of the formula RHC(COOY) 0112mm) (CN)N= NC(CN) (R1) crncwooso HR where Y is a monovalent cation, R1 is a hydrocarbon radical of 1-6 carbons, and R is a member of the class consisting of hydrogen and hydrocarbon radicals of 1-6 carbons.

2. An azo compound of the formula RHC(COOY) CHaC (R1) (CN) N NC(CN) (R1) CH2C(COOY) HR whereY is a monovalent cation, R1 is an organic radical of 1 to 6 carbons and R is a hydrocarbon radical of one to six carbons.

3. A compound REFERENCES CITED The following references are of record in the iven for clearness of understanding only and 30 fi 0! this P Beilstein, 4th edition, vol. 4, 1st Suppl, page 66.

Beilstein, 4th edition, vol. 4, page 563. 

1. AN AZO COMPOUND OF THE FORMULA 